1. Field of the Invention
The present invention relates to a method for preparing N-fluoropyridinium salt. More particularly, the present invention relates to a method for preparing N-fluoropyridinium salt with a high yield.
2. Description of the Related Art
In reactions with organic compounds, fluorine, contrary to chlorine, bromine and iodine, reacts very violently, readily giving rise to the fission of the C--C bond of organic compounds and in cases where the reaction is excessively violent, fire or explosion in turn can break out.
For the purpose resolving the above problem, a fluorinating agent which can introduce fluorine to organic compounds under mild conditions has been developed. The present applicant has earlier found that N-fluoropyridinium salt obtained by reacting pyridine compounds with Br nsted acids or Lewis acids is an excellent fluorinating agent which satisfied these requirements (Japanese Patent Publication No.2-33707). Having high reactivity and selectivity to a variety of organic compounds, the N-fluoropyridinium salt is very useful for preparing fluorocompounds.
However, there is a problem in that the above mentioned Japanese Parent's method for preparing N-fluoropyridinium salt only produces the desired compound with a low yield. Therefore, a more improved method for preparing the same on an industrial scale is required.
As a result of intensive research to overcome this problem, the present inventors have found surprisingly that the use of an amount of a pyridine compound greater than an equimolar amount of a Br nsted acid improves the yield remarkably to achieve the present invention.